Paint / Moisture in Bathroom

Bathroom Ceiling. It's just the perimeter of the ceiling about 1/4 + 1/16" or so the paint is loosening from the ceiling. In a couple of places, it has come off, in the remainder it just looks suspect. Taking a taping knife to it, but the paint does not come loose...but I know it's somewhat loose. And it's only the edges....

I plan to just take a sander, sand it with 120 grit ....mud blend if it's bad and then prime/paint.

Has anyone come across such a issue. I don't think it's a moisture issue in the bathroom....but I can't think of anything else that would be causing this...

Scraping it with a taping knife is not knocking it loose/loose.
It's not blistering but I can ~see~ that it's not 100% secure....

So before I plan to repaint, it's only as good as the base it's on.
I don't mind destroying the edges to get to the point where I can mud and make it clean...

Just can't put my finger on WHAT is causing the issue.
If it was moisture, I would assume that other areas of the ceiling would blister...
The only issue is as described. Just 1/4- 1/16"+ around the entire edge .

Did you use premixed mud (it can resoften if it gets damp)? Do you have and use an exhaust fan? What kind of primer and paint did you use? In a bathroom, you want a good sealer/primer and at least a semigloss paint (that's a bit more moisture resistant) than a flat paint.

I think any paint which does not scrape off is adhered well enough to hold another coat. Hand sand to feather the edges if you must. Taking an electric sander to a ceiling is a messy job.
Moisture is the enemy.

If I had to guess, the base primer was probably 8 year old BM Regal (note the current B Regal lineup is not the *old skool* Regal lineup). The exterior paint was Muralo Ceramic or Pratt & Lambert. Overall, the paint has held up and I've noticed the starting to possibly chalk corners about 2 years ago.

Bathroom is finished tile floor to ceiling. The only paint is the ceiling...

I may just try hand sanding, using a Zinnsers *paint/primer* that is meant for possibly ~loose paint~, paint 2X coats of that and then paint away....

I've got to play with a test patch and see how well it goes.
I hate working facing up ;-)